Atmospheric models of flare stars

Mauas, P. J. D.; Falchi, A.; Falciani, R.

doi:10.1007/3-540-55246-4_137

Cited by 31 publications

(50 citation statements)

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“…The good correlation suggests that both features probably originate from the same region within the chromosphere. This is in contrast with previous observations and modelling of Ca II, Mg II and Hα emission in M dwarfs which implied that the emission in those lines was coming from different chromospheric regions (Mauas & Falchi 1994;Giampapa, Worden & Linsky 1982). An extensive study of He D3 in G and K stars by Saar et al (1997) suggested formation in the upper chromospheres of those stars, and good correlation of the He D3 flux with those of Ca II and C IV (similar to our result here for Hα).…”

Section: Activitycontrasting

confidence: 99%

The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History

Gizis

Reid

Hawley

2002

The Astronomical Journal

311

284

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We present high-resolution echelle spectroscopy of 676 nearby M dwarfs. Our measurements include radial velocities, equivalent widths of important chromospheric emission lines, and rotational velocities for rapidly rotating stars. We identify several distinct groups by their Hα properties, and investigate variations in chromospheric activity amongst early (M0-M2.5) and mid (M3-M6) dwarfs. Using a volume-limited sample together with a relationship between age and chromospheric activity, we show that the rate of star formation in the immediate Solar Neighbourhood has been relatively constant over the last 4 Gyr. In particular our results are inconsistent with recent large bursts of star formation. We use the correlation between Hα activity and age as a function of colour to set constraints on the properties of L and T dwarf secondary components in binary systems. We also identify a number of interesting stars, including rapid rotators, radial velocity variables, and spectroscopic binaries.1 Observations were made at the 60-inch telescope at Palomar Mountain which is jointly owned by the California Institute of Technology and the Carnegie Institution of Washington -4were increased to as much as 1800 seconds.Data were extracted using the FIGARO echelle software (Tomaney & McCarthy, private communication). Wavelength calibration was determined from a 300-second exposure of a Th-Ar lamp taken at the beginning of each night. After each observation of a target star, a short (45 second) exposure of the arc lamp was taken at the same telescope position in order to remove instrumental flexure. The spectra were not flux calibrated. Radial VelocitiesRadial velocities were determined by cross-correlation against reference M dwarfs from Marcy & Benitz (1989 -MB89). The latter velocities are accurate to better than 0.23 kms −1 , a factor of five higher than the accuracy of our own observations (as discussed further below). For the bright, early M dwarfs (TiO5> 0.5) we used the standard echelle FIGARO cross-correlation program. Each order was correlated with the velocity standards, and the average radial velocity from all the orders was determined. The arc lamp exposures, taken adjacent to each program star observation, were also cross-correlated, providing a correction for flexure. This procedure did not provide reliable velocities for faint, late-type M dwarfs. The lower signal-to-noise at blue wavelengths led to a higher potential for bias from the effects of telluric absorption and night sky lines. We were able to obtain reasonable results for those stars by individually computing the cross-correlation for each order and combining those measurements to find the median radial velocity. This procedure was used for all stars with TiO5≤ 0.5. Figure 1 plots the rms dispersion about the mean radial velocity for all M dwarfs with at least four measurements. The distribution suggests a typical internal accuracy of 1.5 kms −1 .We can determine our external errors by comparison with previous high accuracy velocity studies of M dwarfs....

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Section: Activitycontrasting

confidence: 99%

The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History

Gizis

Reid

Hawley

2002

The Astronomical Journal

311

284

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“…For a given distribution of temperature with height, we self‐consistently computed non‐local thermodynamic equilibrium (non‐LTE) populations for 15 levels of H, 13 of He i , six of He ii , 15 of Fe i , eight of Ca i , five of Ca ii , seven of Mg i , six of Mg ii , 21 of Si i , eight of Na i and six of Al i . The atomic models we used for H and Ca ii are described in Mauas et al (1997) and Falchi & Mauas (1998). The Ca ii lines and Lyα were computed using partial redistribution, as it has been done in previous chromospheric models (like, for example, the Vernazza et al 1981 solar models).…”

Section: The Chromospheric Modelsmentioning

confidence: 99%

“…Spatial inhomogeneities characteristic of magnetically active stars, like star‐spots or active regions, cannot be resolved on the stellar surface. The models presented here, however, can be used as a first step to build two component models as was done, for example, by Mauas & Falchi (1996).…”

Section: The Chromospheric Modelsmentioning

confidence: 99%

“…Semi‐empirical models of the dM star AD Leo in its quiescent state and during a flare were built by Mauas & Falchi (1994, 1996). Subsequently, models of two ‘basal’ (i.e.…”

Section: Introductionmentioning

confidence: 99%

“…Subsequently, models of two ‘basal’ (i.e. inactive) stars of the same spectral type, Gl 588 and Gl 628, were constructed by Mauas et al (1997).…”

Section: Introductionmentioning

confidence: 99%

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Chromospheric changes in K stars with activity

Vieytes

Mauas

Díaz

2009

Monthly Notices of the Royal Astronomical Society

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12 years of stellar activity observations in Argentina

Mauas¹,

Buccino²,

Díaz³

et al. 2011

Proc. IAU

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Abstract. We present an observational program we started in 1999, to systematically obtain mid-resolution spectra of late-type stars, to study in particular chromospheric activity. In particular, we found cyclic activity in four dM stars, including Prox-Cen. We directly derived the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigated the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar color, and it is not always preserved when simultaneous observations of a particular star are considered. We also used our observations to model the chromospheres of stars of different spectral types and activity levels, and found that the integrated chromospheric radiative losses, normalized to the surface luminosity, show a unique trend for G and K dwarfs when plotted against the S index.

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Atmospheric models of flare stars

Cited by 31 publications

References 1 publication

The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History

The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History

Chromospheric changes in K stars with activity

12 years of stellar activity observations in Argentina

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